1. Field
This invention relates to temperature controlled apparatus, and more particularly to temperature controlled apparatus using evaporative cooling liquids and large contact pressures induced and magnified from the liquid vapor pressures.
2. Prior Art
In conventional temperature controlled apparatus, for example, semiconductor devices particularly power devices such as power transistors, silicon controlled rectifiers, thyristers, and triacs, heat dissipation is always a very serious problem. The heat generation in the device chip at the PN junction through, for example, ohmic heating, must be conducted away through solder layers at the bottom substrate or top leads. The top leads usually do not have sufficient heat capacity or conducting power. The bottom substrate is often a ceramic disk to achieve electrical isolation. In addition, the solder layers are usually of intermetallic lead-tin alloys, which are low in thermal conductivity. Further, solder layers often dissolve gold, nickel, and silicon from the chip. Such dissolutions cause further increases in thermal resistance in the solder layers. Even worse, because of the thermal expansion mismatch between the chip and the solder layer or substrate, the solder layers are often separated from the chip and/or substrate. Thermally insulating cracks are then formed rendering efficient cooling impossible.
Recently, "translucent" devices are developed that have metal disks in direct thermal contact with the semiconductor chip. The metal disks are cooled by evaporative liquid cooling with, e.g., 3M's "fluorinert electronic liquids" Nos. FC 40, 43, 48, 70, 72, 75, 77, 78, and 104. These liquids have somewhat different physical and electrical properties but boil in the range of 2.5 to at least 56.degree. C., and are electrically and chemically inert relative to the silicon chip.
However, to achieve high dissipation rates, high pressures must be continuously applied through the metal disks to the silicon chip. Such continuous, high pressures often result in physical and electrical failures of the silicon chips.
Accordingly, an object of this invention is to provide improved temperature controlled apparatus;
A further object of the present is to provide improved temperature controlled apparatus and methods for improved heat dissipation in these apparatus;
A broad object of this invention is to provide temperature controlled apparatus whose heat dissipation rate is automatically regulated according to the temperature and/or electrical load on the device chip in these apparatus;
A further object of the invention is to achieve high heat dissipation rates without having high pressures continuously applied onto the chip;
Another broad object of the invention is to regulate the chip-to-substrate thermal conductance according to the load on the semiconductor chip;
Yet another object of the invention is to employ evaporative liquid and regulated heat dissipation rates from the chip through automatically changed, contact pressures and thermal conductance between the chip and substrate.